FIRST PRINCIPLES OF CON FORMA TION. 



by a short trunk and long extremities. I am here assuming 

 that the length of the body is taken comparatively with 

 that of the legs, and without reference to the proportions 

 of the body itself. 



We may also observe from the photographs before us, 

 that the limbs of speedy quadrupeds are proportionately as 

 slender as they are long, and that those exhibiting strength 

 are as thick as they are short. 



I may explain that muscles are the active and essential 

 part of the machinery used by animals in locomotion, bones 

 being merely passive agents. In fact, there are myriads of 

 the lower animals which move about with considerable 

 speed by means of their muscles, but which have no bones 

 of any kind. 



Marey's Law. — The foregoing observations will prepare 

 us for the law cited by Professor Marey in La Machine 

 Animale, which states that muscles of speed are long and 

 slender, and those of strength are short and thick. This 

 distinguished Frenchman gives as instances the long breast- 

 bones of birds — such as the snipe and partridge — which can 

 move their wings with great rapidity, and the short ones of 

 hovering birds — such as the eagle and albatross — which can 

 overcome the immense resistance of the air upon which the 

 large area of their pinions presses, only with slow, but very 

 powerful strokes. The expanse of the outspread wings of 

 birds of quick stroke — such as wild pigeon and partridge — is 

 of far less comparative size than is that of those of hovering 

 birds. The relative speed with which these birds can cleave 

 the air does not, of course, affect the question of the form 

 and action of their muscles. 



